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Systematic mapping of fragile X granules in the mouse brain reveals a potential role for presynaptic FMRP in sensorimotor functions.

Loss of Fragile X mental retardation protein (FMRP) leads to Fragile X syndrome (FXS), the most common form of inherited intellectual disability and autism. Although the functions of FMRP and its homologs FXR1P and FXR2P are well studied in the somatodendritic domain, recent evidence suggests that this family of RNA binding proteins also plays a role in the axonal and presynaptic compartments. Fragile X granules (FXGs) are morphologically and genetically defined structures containing Fragile X proteins that are expressed axonally and presynaptically in a subset of circuits. To further understand the role of presynaptic Fragile X proteins in the brain, we systematically mapped the FXG distribution in the mouse central nervous system. This analysis revealed both the circuits and the neuronal types that express FXGs. FXGs are enriched in circuits that mediate sensory processing and motor planning-functions that are particularly perturbed in FXS patients. Analysis of FXG expression in the hippocampus suggests that CA3 pyramidal neurons use presynaptic Fragile X proteins to modulate recurrent but not feedforward processing. Neuron-specific FMRP mutants revealed a requirement for neuronal FMRP in the regulation of FXGs. Finally, conditional FMRP ablation demonstrated that FXGs are expressed in axons of thalamic relay nuclei that innervate cortex, but not in axons of thalamic reticular nuclei, striatal nuclei, or cortical neurons that innervate thalamus. Together, these findings support the proposal that dysregulation of axonal and presynaptic Fragile X proteins contribute to the neurological symptoms of FXS.

Pubmed ID: 22522693

Authors

  • Akins MR
  • Leblanc HF
  • Stackpole EE
  • Chyung E
  • Fallon JR

Journal

The Journal of comparative neurology

Publication Data

November 1, 2012

Associated Grants

  • Agency: NIDA NIH HHS, Id: F32 DA021501
  • Agency: NICHD NIH HHS, Id: HD052083
  • Agency: NIMH NIH HHS, Id: K99 MH090237
  • Agency: NIMH NIH HHS, Id: MH090237
  • Agency: NINDS NIH HHS, Id: P01 NS039321
  • Agency: NCRR NIH HHS, Id: P20 RR015578
  • Agency: NICHD NIH HHS, Id: R01 HD052083
  • Agency: NIMH NIH HHS, Id: T32 MH020068

Mesh Terms

  • Animals
  • Blotting, Western
  • Brain
  • Cytoplasmic Granules
  • Fragile X Mental Retardation Protein
  • Fragile X Syndrome
  • Immunohistochemistry
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Presynaptic Terminals